These were believed struck by or for Joseph J. Mickley from dies sold by the mint as scrap. They were struck from the 1811 Breen 2 obverse and the 1802 Breen 2 reverse. Both dies are heavily rusted.
The 2 dies were offered, along with other old dies, in an 1878 Mason & Company sale of Mickley items where the Mint confiscated them for destruction.
The first occurrence for one of these appears to be lot 493 of Edward Cogan's Joseph N.T. Levick sale of December 1859 where it was described as "1811 Half Cent, different reverse, very rare type, fine".
About a dozen are believed known.
Photo courtesy of Superior from their June 2002 sale.